Savaging

Proper care of piglets by a mother gilt or sow depends on sanitary conditions and a comfortable environment.

Savaging is a term used in the study of ethology that refers to aggressive behaviour displayed by the mother towards the offspring. Aggressive behaviour includes being rough with, injuring, biting, attacking, crushing and killing (maternal infanticide) of the offspring. While savaging behaviour has been seen in multiple species, it is predominantly demonstrated in domestic pigs (Sus scrofa domesticus). As the definition of savaging is so broad, research on the prevalence of savaging behaviour varies with reports of little savaging of offspring to savaging of offspring up to the 20th percentile. Prevalence of aggressive, non-fatal savaging is greater in gilts as piglet-focused aggression is more frequent in young animals than sows.[1] Occurrence of savaging demonstrated by sows is greater if the sow has previously savaged her offspring either as a gilt or sow. Savaging behaviour usually occurs during the first two days after parturition.[2] Prevalence of savaging is similar among first and second farrowing cycles.[1] Savaging behaviour has a significant impact on both agricultural economy and animal welfare which is why it is currently a subject of interest in the pig industry.

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There exist multiple environmental factors that increase the rate of savaging demonstrated by pigs. It has been shown that human attitudes and behaviour can affect the behaviour of domestic pigs. For example, annoyance and transmission of emotions can occur in gilts and sows when a new worker enters the farrowing rooms and makes excessive noise, does not feed the animals in a timely manner and/or is frustrated/annoyed. Research suggests that maternal behaviour may improve when workers and pigs are familiar with their environment and on a set schedule.[1] Another environmental factor that has been examined is the amount of time spent by humans in the farrowing room. Decreased disturbance of the sows by human intrusions during farrowing has indicated a decrease in savaging behavior.[3] A study by Gonyou and Harris found that increasing light exposure in the farrowing rooms to 16–24 hours per day decreased piglet deaths due to savaging. A further environmental cause of savaging may be the shock mothers feel upon the arrival of the piglets. Piglet arrival can cause fear and alarm in gilts and sows as a new and unfamiliar stimulus has been presented.[3] Some studies have found evidence of increased savaging rates in larger litter sizes as well.[1]

It has been proposed that the degree of aggressive behaviour displayed prior to farrowing cycles by sows and gilts predicts whether the offspring will be savaged and to what extent.[4] Evidence has also been found that savaging sows may be genetically less likely to crush piglets, which lends to the existing research supporting that savaging sows can be competent mothers. High levels of oestradiol at postpartum and high levels of pre-farrowing oestradiol to progesterone ratios in gilts show more savaging behaviour to piglets. Additionally, low plasmaoxytocin during the immediate postpartum period shows an increase in savaging behaviour.[5]Heritability estimates of 0.11 and 0.25 from half-sib analyses have demonstrated that selection against sow savaging of pigs is possible; however, it may be slow to show effectiveness.[6]

The pig industry is investing in research regarding savaging behaviours in hopes to diminish the losses they face when gilts and sows commit infanticide. Sedation techniques following birth have prevented savaging; however, in many cases, the onset of aggression is merely delayed.[4] The industry has also attempted to avoid savaging behavior by limiting reproduction in gilts and sows that have previously savaged their offspring. Efforts to eliminate the behavior include additional care and attention to the mother pig during her farrowing cycles.

Savaging of offspring by the biological mother has been reported in multiple species including farmed silver foxes, farmed wild boar and domestic breeds of farmed pigs.[4] Though aggressive savaging behaviour is demonstrated by other species, it is most commonly used to describe pig aggression. Research has shown that primiparous silver foxes demonstrate savaging shortly after birth with a 37% chance of killing the offspring through bite wounds.[7] Silver foxes have been shown to engage in savaging behaviour followed by infanticide and cannibalism of the offspring.[7] Savaging in wild boars has been found to have genetic significance as different genetic lines have produced varying degrees of savaging.[8] Wild boars have shown aggression after parturition towards their offspring; however, they have lower infanticide rates than other species.